Alzheimer's disease is a common neurodegenerative disease affecting the elderly, resulting in progressive memory impairment, loss of language and visuospatial skills, and behavior deficits. Clinical, genetic, epidemiological and biochemical evidence suggest that dysfunctional cholesterol metabolism is implicated in the pathogenesis of Alzheimer's Disease. Hypercholesterolemia and low levels of high density lipoprotein are well-established risk factors for Alzheimer's Disease. It has been suggested that vascular, genetic and amyloid factors, in combination with diet and lifestyle, contribute to the cause and progression of Alzheimer's Disease. Hooijmans et al, Eur J Pharmacol 585 (2008), 176-196.
The liver X receptor (LXR) is a member of the nuclear receptor family of transcription factors, and is a part of the cholesterol regulation pathway. There are two identified isoforms of LXRs. LXRu is found in liver, intestine and in macrophages, while LXR3 is widely expressed in many tissues and is considered a ubiquitous receptor. Typically, the activity of nuclear receptors is controlled by small lipophilic moieties, such as hormones, fatty acids, bile acids, cholesterol precursors and oxysterols. Lala, Curr Opinions Invest Drugs 2005, 6:934-943. Cholesterol precursors such as desmosterol and oxysterols are known to bind and activate LXRs.
LXRs have demonstrated a role in the physiological metabolism of lipid and cholesterol, and thus are believed to have an important role in metabolic disorders such as hyperlipidemia and atherosclerosis. Activation of LXRs reduces cholesterol absorption, thereby reducing the ability of the body to take up cholesterol. Consistently, deletion of LXRs in mice leads to impaired cholesterol and bile acid metabolism. See Peet et al, Cell 1998, 93(5): 693-704. Activation of LXRs also increase peripheral cholesterol efflux systems, and impact the elimination of cholesterol by regulating cholesterol excretion into bile. See Cao et al, Drug News Perspect 20004, 17(1), 35-41.
LXRs also regulate lipid homeostasis in the brain. The connection between metabolic disorders and Alzheimer's Disease suggests that LXRs may have a role in the Alzheimer's disease pathway. Activation of LXRs also inhibit inflammation and pro-inflammatory expression in the body. Zelcer et al, J Clin Invest 2006, 116:3 (607-614). Thus, LXRs may serve as targets for the treatment of inflammatory diseases. However, activation of hepatic LXRα is believed to be the underlying cause of liver steatosis and hyperlipidemia associated with dual LXRα/β small agonist molecules developed to date.
LXRs have also been proposed as possible therapeutics to treat a number of cancers e.g. prostate, breast, ovarian, melanoma, pancreas, lung, colon and hematological malignancy (Lin, C-Y and Gustafsson, J-A, (2015) Nature Reviews Cancer 15, 216-224).
LXRβ is the predominant brain isoform. See Song et al, Ann NYAcad Sci 195, 761:38-49. LXRβ knockout male mice demonstrated adult-onset motor neuron degeneration. (Andersson et al, Proc Nat'l Acad Sci USA 2005, 8; 1902(1)):3857-3862), and the LXRα and LXRβ double knockout mice develop neurodegenerative changes in brain tissue. (Wang et al, Proc Natl Acad Sci USA. 2002, 99(21):13878-83). Therefore development of selective LXRβ agonists could be a therapeutic approach to neurodegenerative diseases such as AD and avoid the peripheral adverse lipid effects that have been linked to LXRα.
Applicants have now discovered a series of LXRβ selective agonists. Thus, the compounds of the invention, which are selective LXRβ agonists, may be useful in the treatment of Alzheimer's disease, inflammatory diseases, and diseases characterized by defects in cholesterol and lipid metabolism.